pboling · Sep 18, 2026 · Sep 18, 2026 · Sep 18, 2026 · Sep 18, 2026 · Sep 18, 2026
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -133,6 +133,7 @@ jobs:
           cat > ${{ env.BUNDLE_GEMFILE }} << 'EOF'
           source 'https://gem.coop'
           gem 'rake'
+          gem 'bigdecimal', '4.1.3'
           EOF
 
       - name: Run setup-ruby-flash with bundler-cache
@@ -155,6 +156,8 @@ jobs:
           bundle check --gemfile "$BUNDLE_GEMFILE"
           echo "==> Smoke a Rake:"
           bundle exec rake -T
+          echo "==> Test native extension:"
+          bundle exec ruby -rbigdecimal -e 'puts BigDecimal("1.23")'
 
   # Test the action with ore gem installation (Compiled Extensions)
   test-action-with-ore-compiled:

diff --git a/action.yml b/action.yml
@@ -683,6 +683,12 @@ runs:
           fi
         fi
 
+        # On Windows, fix clean_install.rs to use forward slashes in make sitearchdir/sitelibdir arguments
+        # so make's /bin/sh recipe execution does not unescape backslashes.
+        if [ "$RUNNER_OS" = "Windows" ] && [ -f crates/rv/src/commands/clean_install.rs ]; then
+          sed -i 's/tmp_dir\.path()/tmp_dir.path().as_str().replace(\x27\\\\\x27, "\/")/g' crates/rv/src/commands/clean_install.rs || true
+        fi
+
         # Build rv using cargo
         cargo build --release -p rv
 
@@ -950,7 +956,169 @@ runs:
           echo "GEM_HOME=$ACTUAL_GEM_HOME_WIN" >> "$GITHUB_ENV"
           echo "GEM_PATH=$ACTUAL_GEM_PATH_WIN" >> "$GITHUB_ENV"
           [ -n "$RUBY_ROOT" ] && echo "RUBY_ROOT=$(cygpath -m "$RUBY_ROOT")" >> "$GITHUB_ENV"
+
+          # Enable MSYS2 / MinGW DevKit for compiling native C extension gems
+          RIDK_CMD="$RUBY_BIN_DIR/ridk.cmd"
+          if [ -f "$RIDK_CMD" ]; then
+            echo "Enabling MSYS2 DevKit via ridk..."
+            RIDK_OUTPUT=$(cmd.exe /c "set MAKE=make && \"$(cygpath -w "$RIDK_CMD")\" enable" 2>/dev/null || true)
+            while IFS='=' read -r key val; do
+              val=$(echo "$val" | tr -d '\r')
+              key=$(echo "$key" | tr -d '\r')
+              case "$key" in
+                PATH)
+                  IFS=';' read -ra ADDR <<< "$val"
+                  for p in "${ADDR[@]}"; do
+                    if [ -n "$p" ] && [ -d "$p" ]; then
+                      echo "$p" >> "$GITHUB_PATH"
+                      PATH="$p:$PATH"
+                    fi
+                  done
+                  ;;
+                MSYSTEM|MINGW_PACKAGE_PREFIX|RI_DEVKIT|PKG_CONFIG_PATH|ACLOCAL_PATH|MANPATH)
+                  echo "$key=$val" >> "$GITHUB_ENV"
+                  export "$key=$val"
+                  ;;
+              esac
+            done <<< "$RIDK_OUTPUT"
+            echo "MAKE=make" >> "$GITHUB_ENV"
+            export MAKE=make
+          elif [ -d "C:/msys64" ]; then
+            echo "Enabling pre-installed MSYS2 DevKit..."
+            MAJOR_VERSION=$(echo "$FULL_RUBY_VERSION" | cut -d. -f1)
+            MINOR_VERSION=$(echo "$FULL_RUBY_VERSION" | cut -d. -f2)
+            if [ "$MAJOR_VERSION" -ge 4 ] || ([ "$MAJOR_VERSION" -eq 3 ] && [ "$MINOR_VERSION" -ge 1 ]); then
+              TOOLCHAIN="ucrt64"
+            else
+              TOOLCHAIN="mingw64"
+            fi
+            if [ -d "C:/msys64/$TOOLCHAIN/bin" ]; then
+              echo "C:\\msys64\\$TOOLCHAIN\\bin" >> "$GITHUB_PATH"
+              PATH="/c/msys64/$TOOLCHAIN/bin:$PATH"
+            fi
+            if [ -d "C:/msys64/usr/bin" ]; then
+              echo "C:\\msys64\\usr\\bin" >> "$GITHUB_PATH"
+              PATH="/c/msys64/usr/bin:$PATH"
+            fi
+            echo "MAKE=make" >> "$GITHUB_ENV"
+            export MAKE=make
+            echo "RI_DEVKIT=C:\\msys64" >> "$GITHUB_ENV"
+            export RI_DEVKIT="C:\\msys64"
+            echo "MSYSTEM=${TOOLCHAIN^^}" >> "$GITHUB_ENV"
+            export MSYSTEM="${TOOLCHAIN^^}"
+          fi
+
+          # Prepend Ruby bin dir to GITHUB_PATH so Ruby binaries take precedence
           echo "$(cygpath -w "$RUBY_BIN_DIR")" >> "$GITHUB_PATH"
+
+          # Ensure MSYS2 environments inherit the PATH from Windows
+          echo "MSYS2_PATH_TYPE=inherit" >> "$GITHUB_ENV"
+          export MSYS2_PATH_TYPE=inherit
+
+          # Ensure MSYS2 and make can resolve Windows drive paths formatted as /C/... or /D/...
+          # by adding /etc/fstab mount entries, directory junctions, and MSYS2 symlinks.
+          MSYS_ROOTS=()
+          [ -d "/c/msys64" ] && MSYS_ROOTS+=("C:/msys64")
+          [ -d "C:/msys64" ] && MSYS_ROOTS+=("C:/msys64")
+          if [ -n "$RI_DEVKIT" ]; then
+            DEVKIT_POSIX="$(cygpath -m "$RI_DEVKIT" 2>/dev/null || echo "$RI_DEVKIT" | tr '\\' '/')"
+            [ -d "$DEVKIT_POSIX" ] && MSYS_ROOTS+=("$DEVKIT_POSIX")
+          fi
+          GIT_ROOT_POSIX="$(cygpath -m / 2>/dev/null || true)"
+          [ -n "$GIT_ROOT_POSIX" ] && [ -d "$GIT_ROOT_POSIX" ] && MSYS_ROOTS+=("$GIT_ROOT_POSIX")
+          MAKE_BIN=$(command -v make 2>/dev/null || which make 2>/dev/null || true)
+          if [ -n "$MAKE_BIN" ]; then
+            MAKE_ROOT="$(dirname "$(dirname "$(cygpath -m "$MAKE_BIN" 2>/dev/null || echo "$MAKE_BIN" | tr '\\' '/')")")"
+            [ -d "$MAKE_ROOT" ] && MSYS_ROOTS+=("$MAKE_ROOT")
+          fi
+
+          ACTIVE_DRIVES=(C D)
+          for d in E F G H; do
+            d_lower=$(echo "$d" | tr '[:upper:]' '[:lower:]')
+            if [ -d "/$d_lower" ] || [ -d "${d}:/" ]; then
+              ACTIVE_DRIVES+=("$d")
+            fi
+          done
+
+          UNIQUE_MSYS_ROOTS=()
+          for r in "${MSYS_ROOTS[@]}"; do
+            skip=""
+            for u in "${UNIQUE_MSYS_ROOTS[@]}"; do
+              [ "$r" = "$u" ] && skip=1 && break
+            done
+            [ -z "$skip" ] && UNIQUE_MSYS_ROOTS+=("$r")
+          done
+
+          echo "==> Configuring MSYS2 drive mappings for roots: ${UNIQUE_MSYS_ROOTS[*]} and drives: ${ACTIVE_DRIVES[*]}"
+          for root in "${UNIQUE_MSYS_ROOTS[@]}"; do
+            mkdir -p "$root/etc"
+            FSTAB="$root/etc/fstab"
+            touch "$FSTAB"
+            for d in "${ACTIVE_DRIVES[@]}"; do
+              grep -E -q "^${d}:/[[:space:]]+/${d}([[:space:]]|$)" "$FSTAB" 2>/dev/null || echo "${d}:/ /${d} ntfs binary,noacl,auto 1 1" >> "$FSTAB"
+            done
+            echo "Fstab ($FSTAB):"
+            cat "$FSTAB"
+          done
+
+          # Create directory junctions using PowerShell and cmd mklink /J
+          powershell -NoProfile -Command "
+            foreach (\$d in @('C', 'D')) {
+              \$target = \"\${d}:\\\"
+              foreach (\$root in @('C:\\msys64', 'C:\\Program Files\\Git', 'C:\\mingw64', 'C:', 'D:')) {
+                if (Test-Path -LiteralPath \$root) {
+                  \$junction = Join-Path \$root \$d
+                  if (Test-Path -LiteralPath \$junction) {
+                    \$item = Get-Item -LiteralPath \$junction -Force
+                    if (\$item.LinkType -ne 'Junction') {
+                      Remove-Item -LiteralPath \$junction -Force -Recurse
+                    }
+                  }
+                  if (-not (Test-Path -LiteralPath \$junction)) {
+                    New-Item -ItemType Junction -Path \$junction -Value \$target -Force -ErrorAction SilentlyContinue | Out-Null
+                  }
+                }
+              }
+            }
+          " 2>&1 || true
+
+          # Fallback mklink /J for cmd compatibility
+          for d1 in "${ACTIVE_DRIVES[@]}"; do
+            for d2 in "${ACTIVE_DRIVES[@]}"; do
+              cmd.exe /c "if not exist ${d1}:\\${d2} mklink /J ${d1}:\\${d2} ${d2}:\\. " 2>&1 || true
+            done
+          done
+
+          echo "==> Verifying /C and /D paths in Git Bash:"
+          ls -ld /C 2>&1 || echo "ls /C failed"
+          ls -ld /D 2>&1 || echo "ls /D failed"
+          if [ -d "$RUBY_PREFIX" ]; then
+            RUBY_PREFIX_UPPER="$(echo "$RUBY_PREFIX" | sed -E 's/^\/([a-z])\//\/\U\1\//')"
+            echo "Checking Ruby header in uppercase path: $RUBY_PREFIX_UPPER/include/ruby-${MAJOR_MINOR}.0/ruby.h"
+            if [ -f "$RUBY_PREFIX_UPPER/include/ruby-${MAJOR_MINOR}.0/ruby.h" ]; then
+              echo "SUCCESS: Ruby header is accessible via uppercase drive path!"
+            else
+              echo "WARNING: Ruby header not found at $RUBY_PREFIX_UPPER/include/ruby-${MAJOR_MINOR}.0/ruby.h"
+              ls -la "$RUBY_PREFIX/include" 2>&1 || true
+            fi
+          fi
+
+          echo "==> Verifying Win32 junction resolution via PowerShell:"
+          powershell -NoProfile -Command "
+            Get-Item 'C:\C', 'C:\D', 'D:\C', 'D:\D', 'C:\msys64\C', 'C:\msys64\D' -ErrorAction SilentlyContinue | Select-Object FullName, LinkType, Target | Format-Table -AutoSize
+            \$testHeaderD = 'D:\C\Users\runneradmin\AppData\Roaming\rv\rubies\ruby-' + '${FULL_RUBY_VERSION}' + '\include\ruby-' + '${MAJOR_MINOR}' + '.0\ruby.h'
+            \$testHeaderMsys = 'C:\msys64\C\Users\runneradmin\AppData\Roaming\rv\rubies\ruby-' + '${FULL_RUBY_VERSION}' + '\include\ruby-' + '${MAJOR_MINOR}' + '.0\ruby.h'
+            if (Test-Path \$testHeaderD) {
+              Write-Host 'SUCCESS: Header is accessible via Win32 D:\C path:' \$testHeaderD
+            } else {
+              Write-Host 'WARNING: Header not found via Win32 D:\C path:' \$testHeaderD
+            }
+            if (Test-Path \$testHeaderMsys) {
+              Write-Host 'SUCCESS: Header is accessible via MSYS2 C:\msys64\C path:' \$testHeaderMsys
+            } else {
+              Write-Host 'WARNING: Header not found via MSYS2 C:\msys64\C path:' \$testHeaderMsys
+            }
+          " 2>&1 || true
         else
           echo "GEM_HOME=$ACTUAL_GEM_HOME" >> "$GITHUB_ENV"
           echo "GEM_PATH=$ACTUAL_GEM_PATH" >> "$GITHUB_ENV"
@@ -1309,7 +1477,47 @@ runs:
         if [ "${{ steps.cache-bundler-gems.outputs.cache-hit }}" != "true" ]; then
           RV_CI_ARGS+=(--force)
         fi
-        setup_ruby_flash_retry "rv clean-install" "$MAX_RETRIES" "$RV_BIN" ci "${RV_CI_ARGS[@]}"
+        GEM_MANAGER="rv clean-install"
+        if ! setup_ruby_flash_retry "rv clean-install" "$MAX_RETRIES" "$RV_BIN" ci "${RV_CI_ARGS[@]}"; then
+          echo "::warning::rv clean-install failed; falling back to bundle install"
+          GEM_MANAGER="bundle install (rv clean-install fallback)"
+          bundle config set --local path vendor/bundle
+          setup_ruby_flash_retry "bundle install for $GEMFILE" "$MAX_RETRIES" bundle install --gemfile "$GEMFILE" --jobs 4
+        fi
+
+        # On Windows, fix up native extensions if rv clean-install was affected by
+        # the make /bin/sh backslash unescaping issue.
+        if [ "$RUNNER_OS" = "Windows" ] && [ -d "$BUNDLE_PATH_VALUE" ]; then
+          for gem_dir in "$BUNDLE_PATH_VALUE"/ruby/*/gems/*; do
+            [ -d "$gem_dir" ] || continue
+            gem_name_ver="$(basename "$gem_dir")"
+            lib_dir="$gem_dir/lib"
+            ext_src="$gem_dir/ext"
+            [ -d "$ext_src" ] || continue
+
+            while IFS= read -r so_file; do
+              [ -f "$so_file" ] || continue
+              so_name="$(basename "$so_file")"
+              mkdir -p "$lib_dir"
+              if [ ! -f "$lib_dir/$so_name" ]; then
+                echo "Recovered native extension $so_name -> $lib_dir/$so_name"
+                cp -f "$so_file" "$lib_dir/$so_name"
+              fi
+              for ext_api_dir in "$BUNDLE_PATH_VALUE"/ruby/*/extensions/*/*; do
+                [ -d "$ext_api_dir" ] || continue
+                target_ext_dir="$ext_api_dir/$gem_name_ver"
+                mkdir -p "$target_ext_dir"
+                if [ ! -f "$target_ext_dir/$so_name" ]; then
+                  echo "Recovered native extension $so_name -> $target_ext_dir/$so_name"
+                  cp -f "$so_file" "$target_ext_dir/$so_name"
+                fi
+              done
+            done < <(find "$ext_src" -type f \( -name "*.so" -o -name "*.dll" \) 2>/dev/null)
+
+            # Clean up any mangled directory created by make install (e.g., ext/**/D:a* or *:*)
+            find "$ext_src" -mindepth 1 -maxdepth 3 -type d -name "*:*" -exec rm -rf {} + 2>/dev/null || true
+          done
+        fi
 
         END_TIME=$(date +%s)
         ELAPSED=$((END_TIME - START_TIME))
@@ -1337,7 +1545,7 @@ runs:
         echo "| RubyGems Version | $RUBYGEMS_VERSION |" >> $GITHUB_STEP_SUMMARY
         echo "| Bundler Version | $BUNDLER_VERSION |" >> $GITHUB_STEP_SUMMARY
         echo "| rv Version | ${{ steps.rv-version.outputs.version }} |" >> $GITHUB_STEP_SUMMARY
-        echo "| Gem Manager | rv clean-install |" >> $GITHUB_STEP_SUMMARY
+        echo "| Gem Manager | $GEM_MANAGER |" >> $GITHUB_STEP_SUMMARY
         echo "| Platform | ${{ steps.platform.outputs.platform }} |" >> $GITHUB_STEP_SUMMARY
         echo "| Gem Cache Hit | ${{ steps.cache-bundler-gems.outputs.cache-hit }} |" >> $GITHUB_STEP_SUMMARY
         echo "| Gem Install Time | ${ELAPSED}s |" >> $GITHUB_STEP_SUMMARY

diff --git a/scripts/retry.sh b/scripts/retry.sh
@@ -11,7 +11,7 @@
 #
 # "Could not find gem ..." is deliberately absent: a just-published gem can be
 # missing from the index for a few minutes, and retrying is the fix.
-SETUP_RUBY_FLASH_DETERMINISTIC_FAILURES='native extension build failure => Gem::Ext::BuildError|Failed to build gem native extension
+SETUP_RUBY_FLASH_DETERMINISTIC_FAILURES='native extension build failure => Gem::Ext::BuildError|Failed to build gem native extension|Could not compile gem .* extension|CiError\(CompileFailures
 dependency resolution conflict => could not find compatible versions|version solving has failed
 incompatible Ruby version => requires ruby version|conflicting requirements for the ruby version
 Gemfile or gemspec error => there was an error parsing .?gemfile|gemfile syntax error|there was an error while loading .*\.gemspec

diff --git a/spec/action_yml_spec.rb b/spec/action_yml_spec.rb
@@ -32,6 +32,8 @@
     expect(install_step.fetch('if')).to eq("steps.setup-plan.outputs.fast-bundler-install == 'true'")
     expect(install_step.fetch('run')).to include('RV_CI_ARGS=(--gemfile "$GEMFILE")')
     expect(install_step.fetch('run')).to include('"$RV_BIN" ci "${RV_CI_ARGS[@]}"')
+    expect(install_step.fetch('run')).to include('rv clean-install failed; falling back to bundle install')
+    expect(install_step.fetch('run')).to include('bundle install --gemfile "$GEMFILE" --jobs 4')
   end
 
   it 'retries dependency resolution and rv gem installation without changing sources' do
@@ -241,5 +243,8 @@
     setup_script = setup_step.fetch('run')
     expect(setup_script).to include('cygpath -m "$ACTUAL_GEM_HOME"')
     expect(setup_script).to include('cygpath -w "$RUBY_BIN_DIR"')
+    expect(setup_script).to include('RIDK_CMD="$RUBY_BIN_DIR/ridk.cmd"')
+    expect(setup_script).to include('Enabling MSYS2 DevKit via ridk...')
+    expect(setup_script).to include('mklink /J')
   end
 end
diff --git a/spec/retry_sh_spec.rb b/spec/retry_sh_spec.rb
@@ -95,6 +95,9 @@ def classify(line)
 
   it 'recognizes each deterministic failure category' do
     expect(classify('Gem::Ext::BuildError: ERROR')).to eq('native extension build failure')
+    warning = "Warning: Could not compile gem racc-1.8.1's extension ext/racc/cparse/extconf.rb. Got exit code 2."
+    expect(classify(warning)).to eq('native extension build failure')
+    expect(classify('Error: CiError(CompileFailures { gem: "racc-1.8.1" })')).to eq('native extension build failure')
     expect(classify('version solving has failed.')).to eq('dependency resolution conflict')
     expect(classify('nokogiri-1.18.0 requires ruby version >= 3.2')).to eq('incompatible Ruby version')
     expect(classify('[!] There was an error parsing `Gemfile`: syntax error')).to eq('Gemfile or gemspec error')